GTi6 Tyre choice

[Graeme H]

3.3% out

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Speedo says 100kph, you are actually doing 103.3kph. Careful of those speed cameras mate.

That's only true if the speedo was accurate in the first place.
My speedo says 100 when the GPS says 96 (on the original tyres), so that extra 3.3% would make it about right.

[Bobomacho]

This is true.
Im going to weakly back my argument that your gps is wrong due to Perth and something i made up called satellite parralax.

[Wintermute]

I don't trust the GPS Mine sometimes agrees with the speedo and sometimes it doesn't. It seems to vary depending on the terrain. On a trip to Newcastle it will vary by 3 or 4KM/H either side of what the speedo is saying.

I thought that my speedo read higher than actual after a trip to Melbourne. The radars on the 110 freeways down there allways said I was doing under the limit by about 6KM/H On the way back to Sydney I decided that if it was 6KM/H under I could safely sit on 120 in the 110 zone. As I got closer to Sydney I felt that It seemed to be too early. I timed the next 120KM and it took me exactly 1 hour. So the speedo was spot on!

Tony.

[BradlehGordz]

When i had oe tyres on, this check your speed signs and roadwork signs that show your speed, it consistently showed my speedo was 5 kms out, so i was doing 95 but my speedo read 100
So wouldn't that just make me speedo more accurate as said before?

[Graeme H]

I timed the next 120KM and it took me exactly 1 hour. So the speedo was spot on!

How did you measure the 120km distance?
If it was by the odometer, then that should match your speedo because they are part of the same instrument.

[Graeme H]

I don't trust the GPS Mine sometimes agrees with the speedo and sometimes it doesn't. It seems to vary depending on the terrain. On a trip to Newcastle it will vary by 3 or 4KM/H either side of what the speedo is saying.

Thanks for this, very useful information.

I don't have experience with GPS - I just used one to check the speedo. I know they are affected by curves and so on, so tested it on a straight section of freeway where it had time to stabilise. But it's interesting to know that it might still have been different on another stretch of road.

My previous car's speedo (Honda) always matched the Police check signs, but my 206 is always 4km/h over them. That sort of backs up the GPS test.

If my speedo is that far out then I suppose my fuel consumption estimates are optimistic too.

Edit to add: I like Bobomacho's explanation too - it sounds like you know Perth well!

[Graeme H]

Back to tyres...

yokohama c-drive and nothing else!

Different cars and different tyre sizes can make a difference, but I was not especially impressed by the C-drive (AC01) on my Honda CRX. They were more than adequate, good to drive on, but they did nothing better than the Yokohama A520 (by then unavailable) to justify lasting only half the distance.

Of course, we're not all seeking the same characteristics from our tyres.